Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide method and apparatus for video coding. In some examples, an apparatus includes processing circuitry for video decoding. The processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information is indicative of an intra block copy mode. The processing circuitry selects, from a set of multiple candidate resolutions, a resolution of a block vector difference for the current block, and determines a block vector of the current block according to the selected resolution of the block vector difference and a block vector predictor of the current block. Then, the processing circuitry reconstructs at least one sample of the current block according to the block vector.

INCORPORATION BY REFERENCE

This present disclosure is a continuation of U.S. application Ser. No.16/182,788, filed Nov. 7, 2018, which claims the benefit of priority toU.S. Provisional Application No. 62/639,862, “METHODS FOR ADAPTIVEMOTION AND BLOCK VECTOR RESOLUTIONS IN IMAGE AND VIDEO COMPRESSION”filed on Mar. 7, 2018. The entire disclosures of the prior applicationsare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In Intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used in as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer bitsare required at a given quantization step size to represent the blockafter entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), benchmark set(BMS). A predictor block can be formed using neighboring samples valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 35 possible predictordirections. The point where the arrows converge (101) represents thesample being predicted. The arrows represent the direction from whichthe sample is being predicted. For example, arrow (102) indicates thatsample (101) is predicted from a sample or samples to the upper right,at a 45 degree angle from the horizontal. Similarly, arrow (103)indicates that sample (101) is predicted from a sample or samples to thelower right of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top right there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in Y dimension (e.g., row index) and its position in Xdimension (e.g., column index). For example, sample S21 is the secondsample in Y dimensions (from the top) and the first (from the left)sample in X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both Y and X dimension. As the block is 4×4 samples insize, S44 is at the bottom right. Further shown are reference samples,that follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted fromprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from same R05. Sample S44 is then predicted from R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves can besometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 a schematic (201) that depicts 65 intra prediction directionsaccording to JEM to illustrate the increasing number of predictiondirections over time.

The mapping of an intra prediction directions bits in the coded videobitstream that represent the direction can be different form videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode to codewords, to complex adaptive schemes involving mostprobably modes and similar techniques. A person skilled in the art isreadily familiar with those techniques. In all cases, however, there canbe certain directions that are statistically less likely to occur invideo content than certain other directions. As the goal of videocompression is the reduction of redundancy, those less likely directionswill, in a well working video coding technology, be represented by alarger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide method and apparatus for video coding.In some examples, an apparatus includes processing circuitry for videodecoding. The processing circuitry decodes prediction information of acurrent block from a coded video bitstream. The prediction informationis indicative of an intra block copy mode. The processing circuitryselects, from a set of multiple candidate resolutions, a resolution of ablock vector difference for the current block, and determines a blockvector of the current block according to the selected resolution of theblock vector difference and a block vector predictor of the currentblock. Then, the processing circuitry reconstructs at least one sampleof the current block according to the block vector.

In an example, the processing circuitry selects, from two candidateresolutions, the resolution for the current block based on a 1-bit flag.

According to an aspect of the disclosure, the processing circuitryselects a first resolution for a first component of the block vectordifference, and selects a second resolution for a second component ofthe block vector difference. For example, the processing circuitryselects the first resolution for the first component of the block vectordifference based on a first flag; and selects the second resolution forthe second component of the block vector difference based on a secondflag.

In some embodiments, the processing circuitry selects the firstresolution for the first component of the block vector difference basedon a first component of the block vector predictor, and selects thesecond resolution for the second component of the block vectordifference based on a second component of the block vector predictor.

In some examples, the processing circuitry selects a default resolutionfrom a set of two resolutions as the first resolution when the firstcomponent of the block vector predictor is smaller than a threshold, andselects a smaller resolution from the set of two resolutions as thefirst resolution when the first component of the block vector predictoris larger than a threshold.

It is noted that, in an example, the processing circuitry adds the blockvector difference to the block vector predictor without rounding theblock vector predictor to calculate the block vector when the blockvector predictor used a different resolution from the selectedresolution. In another example, the processing circuitry rounds theblock vector predictor of the current block to the selected resolutionwhen the block vector predictor has a different resolution from theselected resolution; and adds block vector difference to the roundedblock vector predictor to calculate the block vector.

In some embodiments, the processing circuitry modifies at least one ofthe block vector difference and the block vector predictor to constrainthe block vector in a valid region.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a subset of intra prediction modesin accordance with H.265.

FIG. 2 is an illustration of intra prediction directions according toJEM.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure.

FIG. 10 shows a flow chart outlining a process (1000) according to anembodiment of the disclosure.

FIG. 11 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (515), so as to createsymbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601)(that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721) and anentropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intra,the general controller (721) controls the switch (726) to select theintra mode result for use by the residue calculator (723), and controlsthe entropy encoder (725) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (721) controls the switch(726) to select the inter prediction result for use by the residuecalculator (723), and controls the entropy encoder (725) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients. In various embodiments, thevideo encoder (703) also includes a residue decoder (728). The residuedecoder (728) is configured to perform inverse-transform, and generatethe decoded residue data. The decoded residue data can be suitably usedby the intra encoder (722) and the inter encoder (730). For example, theinter encoder (730) can generate decoded blocks based on the decodedresidue data and inter prediction information, and the intra encoder(722) can generate decoded blocks based on the decoded residue data andthe intra prediction information. The decoded blocks are suitablyprocessed to generate decoded pictures and the decoded pictures can bebuffered in a memory circuit (not shown) and used as reference picturesin some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (725) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(872) or the inter decoder (880) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(880); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (872). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (871) (datapath not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603) and (703), and thevideo decoders (410), (510) and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603)and (703), and the video decoders (410), (510) and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603) and (603), and the videodecoders (410), (510) and (810) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques for intra picture blockcompensation.

Block based compensation from a different picture is referred to asmotion compensation. Similarly, a block compensation can also be donefrom a previously reconstructed area within the same picture. The blockbased compensation from reconstructed area within the same pictures isreferred to as intra picture block compensation, or intra block copy. Adisplacement vector that indicates the offset between the current blockand the reference block in the same picture is referred to as a blockvector (or BV for short). Different from a motion vector in motioncompensation, which can be at any value (positive or negative, at eitherx or y direction), a block vector has a few constraints to ensure thatthe reference block is available and already reconstructed. Also, insome examples, for parallel processing consideration, some referencearea that is tile boundary or wavefront ladder shape boundary isexcluded.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode, the difference between a block vector and itspredictor is signaled; in the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor), in asimilar way as a motion vector in merge mode. The resolution of a blockvector, in some implementations, is restricted to integer positions; inother systems, the block vector is allowed to point to fractionalpositions.

In some examples, the use of intra block copy at block level, can besignaled using a reference index approach. The current picture underdecoding is then treated as a reference picture. In an example, such areference picture is put in the last position of a list of referencepictures. This special reference picture is also managed together withother temporal reference pictures in a buffer, such as decoded picturebuffer (DPB).

There are also some variations for intra block copy, such as flippedintra block copy (the reference block is flipped horizontally orvertically before used to predict current block), or line based intrablock copy (each compensation unit inside an M×N coding block is an M×1or 1×N line).

FIG. 9 shows an example of intra block copy according to an embodimentof the disclosure. Current picture 900 is under decoding. The currentpicture 900 includes a reconstructed area 910 (grey area) andto-be-decoded area 920 (white area). A current block 930 is underreconstruction a decoder. The current block 930 can be reconstructedfrom a reference block 940 that is in the reconstructed area 910. Theposition offset between the reference block 940 and the current block930 is referred to as a block vector 950 (or BV 950).

Traditionally, motion vector resolution is a fixed value, for example,at ¼-pel (pixel) accuracy in H.264/AVC and HEVC main profile, or at⅛-pel accuracy, etc. In HEVC SCC, the resolution of a motion vector canbe chosen at either 1-integer-pel or ¼-pel. The switch takes place ateach slice. In other words, the resolution of all motion vectors in aslice will be the same.

In some later development, the resolutions of motion vectors can be ateither ¼-pel, 1-integer-pel or 4-integer-pel. In the example of4-integer-pel, each unit represents 4 integer pixels. Therefore, thereare 4 integer pixels distance between symbol “0” to “1”. Also, theadaptivity takes place at block level—motion vectors can choose adifferent resolution block by block.

Aspects of the present disclosure provide methods for adaptive motionvector resolution and block vector resolution in image and videocompression.

A block vector is typically signaled at integer resolution. When theintra block copy is extended to full frame range, thus all thereconstructed area of the current decoded picture can be used as areference, the expense of coding block vector difference will be highfor far away references. Adaptive block vector difference resolution canbe used to improve the coding of block vector difference.

In some examples, multiple block vector resolutions are used for codingof block vectors, and the block vector resolution is switchable at blocklevel. Further, a signaling flag, which may include more than 1-bin whenmore than two possible resolutions are used, is used to tell which ofthe multiple block vector resolutions is used for the block vectordifference of a current block. The possible resolutions include but arenot limited to ⅛-pel, ¼-pel, ½-pel, 1-integer-pel, 2-integer-pel,4-integer-pel, 8-integer-pel, etc. The X-integer-pel means each smallestunit of the symbol represents X integer positions. For example,2-integer-pel means each smallest unit of the symbol represents 2integer positions, 4-integer-pel means each smallest unit of the symbolrepresents 4 integer positions, 8-integer-pel means each smallest unitof the symbol represents 8 integer positions.

In one embodiment, a set of resolutions can be used and a flag can besignaled to indicate which one in the set of resolutions is used. In anexample, the block vector difference resolution set includes tworesolutions, such as 1-integer-pel and 2-integer-pel. Then, a 1-bin (1binary) flag is signaled to choose one resolution from the two possibleresolutions. In another example, the block vector resolution setincludes 1-integer-pel and 4-integer-pel. Then, a 1-bin flag is signaledto choose one from the two possible resolutions.

In another example, the block vector difference resolution set includes1-integer-pel, 2-integer pel and 4-integer-pel. A 1-bin flag is signaledto indicate whether 1-integer-pel resolution is used. If 1-integer-pelis not used, another 1-bin flag is signaled to indicate whether tochoose 4-integer-pel resolution. Different binarization embodiments canbe derived, in a similar way to use either 1-bin or 2-bins to indicatethe resolution choice from 3 possibilities.

In another example, the block vector difference resolution set includes1-integer-pel, 4-integer pel, and 8-integer-pel. A 1-bin flag issignaled to indicate whether 1-integer-pel resolution is used. If1-integer-pel is not used, another 1-bin flag is signaled to indicatewhether to choose 4-integer-pel resolution. Different binarizationembodiments can be derived, in a similar way to use either 1-bin or2-bins to indicate the resolution choice from 3 possibilities.

In another example, the x and y components of a block vector differencecan use different resolutions. For example, the x component of a blockvector difference is at 1-integer-pel resolution while the y componentis at 4-integer-pel resolution. The choice for each component can bemade by explicit signaling (1 flag per component) or by inference. Forexample, the magnitude of the current block's block vector predictor canbe used to infer the resolution. In an example, when the magnitude of acomponent of the block vector predictor is greater than a threshold, theblock vector difference resolution for this component will use largerstep resolution, for example 4-integer-pel resolution; otherwise, thiscomponent will use smaller step resolution, for example 1-integer-pelresolution.

In another example, the x and y components of a block vector differencecan use different resolutions. By default, both components will use afixed resolution, such 1-integer-pel resolution. Component-wiseconditions are setup respectively for the components to decideresolutions. For example, when some component-wise conditions are met,each component can switch to a different resolution by inference. Thecomponents of the predictor will be quantized to correspondingresolutions as well, or just keep its original resolution unchanged. Forexample, one component-wise condition is related to the magnitude of thecurrent block's block vector predictor. By evaluating the magnitude ofthe current block's block vector predictor in each component, theresolution can be inferred for the component. For example, when themagnitude of a component of the block vector predictor is greater than athreshold, the block vector difference resolution for this componentwill use the larger step resolution, for example 4-integer-pelresolution; otherwise, this component will use default step resolution,for example 1-integer-pel resolution. In one specific example, thedefault resolution is 1-integer-pel. A block vector predictor is set tobe (−21, −3) while the threshold for using 4-integer-pel resolution is20 for each component. The decoded block vector difference symbol is (2,2). According to the rule, the x component will be using 4-integer-pelresolution while the y component will be using 1-integer-pel resolution.The predictor will then become (−20, −3) (−21 is rounded to −20) and theblock vector difference will become (8, 2) (due to 4-inter-pel for xcomponent and 1-integer-pel for y component). The final decoded blockvector is (−12,−1) in this example.

Similar examples can be derived using similar derivations in the aboveexamples. In an embodiment, a set of possible resolution is formed, andsignaling flag(s) is used to indicate the selection of resolution blockby block. Also in the above examples, the bins of signaling flag can beeither context coded, or by-pass coded. If using context coding, theblock vector resolution of current block's spatial neighbors can be usedfor context modeling. Or, the resolution of a last coded block vectorcan be used.

According to another aspect of the disclosure, the block vectorpredictor is typically derived from one previously coded block vector ofa neighboring block to the current block. When used as a predictor, thepreviously decoded block vector may have a different resolution as theresolution in the current block. The present disclosure provides methodsto address this issue.

In one embodiment, the original resolution of the block vector predictoris kept unchanged. The decoded block vector difference, in its targetresolution, will be added to the block vector predictor to obtain thefinal decoded block vector. The final decoded block vector will betherefore in a higher resolution of the two resolutions (the originalresolution of the block vector predictor, and the target resolution ofthe decoded block vector difference. For example, the block vectorpredictor is a vector (−11, 0) having 1-integer-pel resolution. Thedecoded block vector difference is a vector (−4, 0) having 4-integer-pelresolution. The decoded block vector will be (−15, 0) having1-integer-pel resolution.

In another embodiment, the original resolution of the block vectorpredictor is rounded to the target resolution of the current block. Thedecoded block vector difference, in its target resolution, will be addedto the block vector predictor. The final decoded block vector will betherefore in a lower precision resolution of the two. For example, theblock vector predictor is a vector (−11, 0) having 1-integer-pelresolution. The decoded block vector difference is a vector (−4, 0)having 4-integer-pel resolution. The block vector predictor will befirstly rounded to a vector (−12, 0) having 4-integer-pel resolutionbefore being added to the decoded block vector difference. The decodedblock vector will be a vector (−16, 0) having 4-integer-pel resolution.

Various rounding techniques can be used. In an example, vectors can berounded to the nearest integer (corresponding to integer symbol values)according to the difference. For example, (−11, 0) having 1-integer-pelresolution is rounded to (−12, 0) having 4-integer-pel resolution, (−13,0) having 1-integer-pel resolution is also rounded to (−12, 0) having4-integer-pel resolution.

In another example, ceiling operation is applied to vectors to round tothe nearest integer (corresponding to integer symbol values) that is notsmaller than current value. For example, (−11, 0) having 1-integer-pelresolution is rounded to (−8,0) having 4-integer-pel resolution, and(−13, 0) having 1-integer-pel resolution is also rounded to (−12, 0)having 4-integer-pel resolution.

In another example, flooring operation is applied to vectors to round tothe nearest integer (corresponding to integer symbol values) that is notlarger than current value. For example, (−11, 0) having 1-integer-pelresolution is rounded to (−12, 0) having 4-integer-pel resolution, and(−13, 0) having 1-integer-pel resolution is also rounded to (−16, 0)having 4-integer-pel resolution.

In another example, vectors are rounded toward zero direction. Forexample, (−11, 0) having 1-integer-pel resolution is rounded to (−8, 0)having 4-integer-pel resolution, and (11, −5) having 1-integer-pelresolution is rounded to (8, −4) having 4-integer-pel resolution.

Aspects of the disclosure also provide techniques to handle boundaryconstrains with the multiple resolutions. In an example, a block vectoris constrained to point to a reference area that is allowed to use intrapicture block compensation. The constraints can includepicture/slice/tile and wavefront boundaries of the allowed referencearea. When multiple resolutions are used, especially when larger than1-integer-pel resolution is used, the boundary constraints should behandled correctly.

In an embodiment, when the block vector (block vectorpredictor+difference) points to a location that is outside the referencearea boundary, a clipping operation is performed to modify one or twocomponents of the block vector back to the edge of the boundary so thatthe modified block vector is a valid one. The clipping operation can bedone without considering the decoded block vector's resolution. Thus,after the modification, the block vector's resolution may be differentfrom its resolution before modification.

In another embodiment, when the block vector (block vectorpredictor+difference) points to a location that is outside the referencearea boundary, a clipping operation is performed to modify one or twocomponents of the vector back towards the edge of the boundary so thatthe modified block vector is a valid one. The clipping operation can bedone with consideration of the decoded block vector's resolution. Thus,after the modification, the block vector's resolution remains the sameas before.

In another embodiment, when the block vector (block vectorpredictor+difference) points to a location that is outside the referencearea boundary, pixels outside the boundary can be represented byextending the pixels at the boundary horizontally or vertically.

In another embodiment, when the block vector (block vectorpredictor+difference) points to a location that is outside the referencearea boundary, the resolution of block vector difference will be changedinto the highest possible precision. For example, a block vectorpredictor is a vector (0, 0) and a block vector difference is a symbol(−5, 0) in 4-integer-pel resolution. The highest possible precision is1-integer-pel. When the decoded block vector is in 4-integer-pelresolution, the block vector will be (−20, 0). If (−20,0) points to alocation outside the left picture boundary, then the decoded blockvector difference will be changed into 1-integer-pel resolution, makingthe decode block vector to be (−5, 0), in which case is a valid vector.This change can help moving the block vector inside the boundary.

According to another aspect of the disclosure, techniques for handlingmultiple resolutions in the block vectors for intra picture blockcompensation can be similarly applied to motion vectors for interpicture block compensation. In some embodiments, multiple motion vectorresolutions are used for coding of motion vectors, and the motion vectorresolution is switchable at block level. Further, a signaling flag,which may include more than 1-bin when more than two possibleresolutions are used, is used to tell which of the multiple motionvector resolutions is used for the motion vector difference of a currentblock. The possible resolutions include but are not limited to ⅛-pel,¼-pel, ½-pel, 1-integer-pel, 2-integer-pel, 4-integer-pel,8-integer-pel, etc. The X-integer-pel means each smallest unit of thesymbol represents X integer positions. For example, 2-integer-pel meanseach smallest unit of the symbol represents 2 integer positions,4-integer-pel means each smallest unit of the symbol represents 4integer positions, 8-integer-pel means each smallest unit of the symbolrepresents 8 integer positions.

In an example, the x and y components of a motion vector difference canuse different resolutions. For example, the x component of a motionvector difference is at 1-integer-pel resolution while the y componentis at 4-integer-pel resolution. The choice for each component can bemade by explicit signaling (1 flag per component) or by inference. Forexample, the magnitude of the current block's motion vector predictorcan be used to infer the resolution. In an example, when the magnitudeof a component of the motion vector predictor is greater than athreshold, the motion vector difference resolution for this componentwill use larger step resolution, for example 4-integer-pel resolution;otherwise, this component will use smaller step resolution, for example1-integer-pel resolution.

In another example, the x and y components of a motion vector differencecan use different resolutions. By default, both components will use afixed resolution, such ¼-pel resolution. Component-wise conditions aresetup respectively for the components to decide resolutions. Forexample, when some component-wise conditions are met, each component canswitch to a different resolution by inference. The components of thepredictor will be quantized to corresponding resolutions as well, orjust keep its original resolution unchanged. For example, onecomponent-wise condition is related to the magnitude of the currentblock's motion vector predictor. By evaluating the magnitude of thecurrent block's motion vector predictor in each component, theresolution can be inferred for the component. For example, when themagnitude of a component of the motion vector predictor is greater thana threshold, the motion vector difference resolution for this componentwill use the larger step resolution, for example 4-integer-pelresolution; otherwise, this component will use default step resolution,for example ¼-pel resolution. In one specific example, the defaultresolution is ¼-pel. A motion vector predictor is set to be (−20.75,−3.75) while the threshold for using 1-integer-pel resolution is 5 foreach component. The decoded motion vector difference symbol is (2, 2).According to the rule, the x component will be using 1-integer-pelresolution while the y component will be using ¼-pel resolution. Themotion vector predictor will then become (−20, −3.75) (e.g., −20.75 isrounded to −20 toward zero direction) and the block vector differencewill become (2, 0.5) (due to 1-inter-pel for x component and ¼-pel for ycomponent). The final decoded block vector is (−18, −3.25) in thisexample.

FIG. 10 shows a flow chart outlining a process (1000) according to anembodiment of the disclosure. The process (1000) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1000) are executed by processing circuitry,such as the processing circuitry in the terminal devices (310), (320),(330) and (340), the processing circuitry that performs functions of thevideo encoder (403), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the video decoder (510), the processing circuitry thatperforms functions of the intra prediction module (552), the processingcircuitry that performs functions of the video encoder (603), theprocessing circuitry that performs functions of the predictor (635), theprocessing circuitry that performs functions of the intra encoder (722),the processing circuitry that performs functions of the intra decoder(872), and the like. In some embodiments, the process (1000) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1000). The process starts at (S1001) and proceeds to(S1010).

At (S1010), prediction information of a current block is decoded from acoded video bitstream. The prediction information is indicative of anintra block copy mode.

At (S1020), a resolution is selected from a set of multiple candidateresolutions for a block vector difference of the current block. In anexample, a resolution flag is received, and the resolution is selectedbased on the flag. In another example, the resolution is determinedbased on inference.

At (S1030), a block vector of the current block is determined accordingto the selected resolution of the block vector difference and a blockvector predictor of the current block.

At (S1040), samples of the current block are constructed according tothe determined block vector. Then the process proceeds to (S1099) andterminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 11 shows a computersystem (1100) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 11 for computer system (1100) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1100).

Computer system (1100) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data-glove (not shown), joystick (1105), microphone(1106), scanner (1107), camera (1108).

Computer system (1100) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1110), data-glove (not shown), or joystick (1105), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1109), headphones(not depicted)), visual output devices (such as screens (1110) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1100) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1120) with CD/DVD or the like media (1121), thumb-drive (1122),removable hard drive or solid state drive (1123), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1100) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1149) (such as, for example USB ports of thecomputer system (1100)); others are commonly integrated into the core ofthe computer system (1100) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1100) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1140) of thecomputer system (1100).

The core (1140) can include one or more Central Processing Units (CPU)(1141), Graphics Processing Units (GPU) (1142), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1143), hardware accelerators for certain tasks (1144), and so forth.These devices, along with Read-only memory (ROM) (1145), Random-accessmemory (1146), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1147), may be connectedthrough a system bus (1148). In some computer systems, the system bus(1148) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1148),or through a peripheral bus (1149). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1141), GPUs (1142), FPGAs (1143), and accelerators (1144) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1145) or RAM (1146). Transitional data can be also be stored in RAM(1146), whereas permanent data can be stored for example, in theinternal mass storage (1147). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1141), GPU (1142), massstorage (1147), ROM (1145), RAM (1146), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1100), and specifically the core (1140) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1140) that are of non-transitorynature, such as core-internal mass storage (1147) or ROM (1145). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1140). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1140) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1146) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1144)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block from abitstream, the prediction information being indicative of an intra blockcopy mode; determining a block vector predictor for the current blockbased on the prediction information; determining a block vectordifference for the current block based on the prediction information;selecting a first candidate resolution as a first resolution for a firstcomponent of the block vector difference in a case that a firstmagnitude of a first component of the block vector predictor isdetermined to be greater than a threshold; selecting a second candidateresolution as the first resolution for the first component of the blockvector difference in a case that the first magnitude of the firstcomponent of the block vector predictor is determined to be not greaterthan the threshold, the second candidate resolution being a higherprecision resolution than the first candidate resolution; determining ablock vector for the current block according to the block vectorpredictor, the block vector difference, and the first resolution for thefirst component of the block vector difference; and reconstructing oneor more samples of the current block according to the block vector. 2.The method of claim 1, further comprising: selecting the first candidateresolution as a second resolution for a second component of the blockvector difference in a case that a second magnitude of a secondcomponent of the block vector predictor is determined to be greater thanthe threshold; and selecting the second candidate resolution as thesecond resolution for the second component of the block vectordifference in a case that the second magnitude of the second componentof the block vector predictor is determined to be not greater than thethreshold.
 3. The method of claim 1, wherein the determining the blockvector comprises: converting the block vector predictor to a convertedblock vector predictor that adopts a resolution setting of the blockvector difference; and determining the block vector according to acombination of the converted block vector predictor and the block vectordifference.
 4. The method of claim 1, wherein the determining the blockvector comprises: converting the block vector difference to a convertedblock vector difference that adopts a resolution setting of the blockvector predictor; and determining the block vector according to acombination of the block vector predictor and the converted block vectordifference.
 5. The method of claim 1, wherein the determining the blockvector comprises: determining a pre-modification block vector accordingto the block vector predictor and the block vector difference; in a casethat the pre-modification block vector is determined to be outside avalid region, determining the block vector by modifying thepre-modification block vector to constrain the block vector in the validregion; and in a case that the pre-modification block vector isdetermined to be in the valid region, setting the pre-modification blockvector as the block vector.
 6. The method of claim 1, wherein the firstcandidate resolution is a 1-pel resolution, and the second candidateresolution is a ¼-pel resolution.
 7. The method of claim 1, wherein thefirst candidate resolution is a 4-pel resolution, and the secondcandidate resolution is a 1-pel resolution.
 8. The method of claim 1,wherein the threshold is 5 pixels.
 9. An apparatus for video decoding,comprising: processing circuitry configured to: decode predictioninformation of a current block from a bitstream, the predictioninformation being indicative of an intra block copy mode; determine ablock vector predictor for the current block based on the predictioninformation; determine a block vector difference for the current blockbased on the prediction information; select a first candidate resolutionas a first resolution for a first component of the block vectordifference in a case that a first magnitude of a first component of theblock vector predictor is determined to be greater than a threshold;select a second candidate resolution as the first resolution for thefirst component of the block vector difference in a case that the firstmagnitude of the first component of the block vector predictor isdetermined to be not greater than the threshold, the second candidateresolution being a higher precision resolution than the first candidateresolution; determine a block vector for the current block according tothe block vector predictor, the block vector difference, and the firstresolution for the first component of the block vector difference; andreconstruct one or more samples of the current block according to theblock vector.
 10. The apparatus of claim 9, wherein the processingcircuitry is further configured to: select the first candidateresolution as a second resolution for a second component of the blockvector difference in a case that a second magnitude of a secondcomponent of the block vector predictor is determined to be greater thanthe threshold; and select the second candidate resolution as the secondresolution for the second component of the block vector difference in acase that the second magnitude of the second component of the blockvector predictor is determined to be not greater than the threshold. 11.The apparatus of claim 9, wherein the processing circuitry is furtherconfigured to: convert the block vector predictor to a converted blockvector predictor that adopts a resolution setting of the block vectordifference; and determine the block vector according to a combination ofthe converted block vector predictor and the block vector difference.12. The apparatus of claim 9, wherein the processing circuitry isfurther configured to: convert the block vector difference to aconverted block vector difference that adopts a resolution setting ofthe block vector predictor; and determine the block vector according toa combination of the block vector predictor and the converted blockvector difference.
 13. The apparatus of claim 9, wherein the processingcircuitry is further configured to: determine a pre-modification blockvector according to the block vector predictor and the block vectordifference; in a case that the pre-modification block vector isdetermined to be outside a valid region, determine the block vector bymodifying the pre-modification block vector to constrain the blockvector in the valid region; and in a case that the pre-modificationblock vector is determined to be in the valid region, set thepre-modification block vector as the block vector.
 14. The apparatus ofclaim 9, wherein the first candidate resolution is a 1-pel resolution,and the second candidate resolution is a ¼-pel resolution.
 15. Theapparatus of claim 9, wherein the first candidate resolution is a 4-pelresolution, and the second candidate resolution is a 1-pel resolution.16. The apparatus of claim 9, wherein the threshold is 5 pixels.
 17. Anon-transitory computer-readable medium storing instructions which whenexecuted by a computer for video decoding cause the computer to perform:decoding prediction information of a current block from a bitstream, theprediction information being indicative of an intra block copy mode;determining a block vector predictor for the current block based on theprediction information; determining a block vector difference for thecurrent block based on the prediction information; selecting a firstcandidate resolution as a first resolution for a first component of theblock vector difference in a case that a first magnitude of a firstcomponent of the block vector predictor is determined to be greater thana threshold; selecting a second candidate resolution as the firstresolution for the first component of the block vector difference in acase that the first magnitude of the first component of the block vectorpredictor is determined to be not greater than the threshold, the secondcandidate resolution being a higher precision resolution than the firstcandidate resolution; determining a block vector for the current blockaccording to the block vector predictor, the block vector difference,and the first resolution for the first component of the block vectordifference; and reconstructing one or more samples of the current blockaccording to the block vector.
 18. The non-transitory computer-readablemedium of claim 17, wherein the instructions, when executed by thecomputer for video decoding, further cause the computer to perform:selecting the first candidate resolution as a second resolution for asecond component of the block vector difference in a case that a secondmagnitude of a second component of the block vector predictor isdetermined to be greater than the threshold; and selecting the secondcandidate resolution as the second resolution for the second componentof the block vector difference in a case that the second magnitude ofthe second component of the block vector predictor is determined to benot greater than the threshold.
 19. The non-transitory computer-readablemedium of claim 17, wherein the determining the block vector comprises:converting the block vector predictor to a converted block vectorpredictor that adopts a resolution setting of the block vectordifference; and determining the block vector according to a combinationof the converted block vector predictor and the block vector difference.20. The non-transitory computer-readable medium of claim 17, wherein thedetermining the block vector comprises: converting the block vectordifference to a converted block vector difference that adopts aresolution setting of the block vector predictor; and determining theblock vector according to a combination of the block vector predictorand the converted block vector difference.